The Effect of Chemical Vapor Deposition Temperature on the

• Main Authors: Lin, Zong-Ping, 林宗平
• Other Authors: Ju-Liang He, Chen-Sen Chang
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/68630770391397877806

碩士 === 逢甲大學 === 材料科學研究所 === 85 === ABSTRACTThe use of chemical vapor deposition (CVD) process as a method of producing large scale and compact components for the infrared transmitting materials has been developed in the last two decades. Among those materials, Zinc Sulphide is applied in domes and windows which requires the transmittance in the wavelength of 8 to 12μm. The low pressure chemical vapor deposition(LPCVD) process's offering advantages over conventional hot-press methods are the high purity, high density the ability of producing large cponents with complex shapes. Properties of CVD materials can be controlled by adjusting process parameters such as working temperature, pressure, degree of supersaturation, flow rate, growth rate, etc. Among which the deposition temperature may be very critical to the subsequent properties including optical properties and mechanical properties. In this study, polycrystalline ZnS infrared transmitting material was prepared by using a horizontal LPCVD reactor. All the process parameters are fixed and deposition temperature is changed from 560 ℃ to 850 ℃ to reveal the effect on microstructure and the subsequent optical and mechanical properties. X-ray diffractometry(XRD), energy- dispersive spectrometry(EDS), optical microscopy(OM) and scanning Electron Microscopy(SEM) were used to reveal the microstructure of the deposits. Hardness value and fracture toughness were determined using Vicker's indentation technique. Erosion rate was measured by solid particle erosion method. The optical properties were measured by using the spectrophotometer with wavelength from 0.35μm to 16μm. Experimental results show that the color of deposited ZnS changes as the deposition temperature changes. The color of the deposit is brown at low temperature while it becomes white and clear with increasing deposition temperature from 560℃ to 850℃. A type of zinc blende structure(β- phase) was found of the deposits all over deposition temperatures with (111) texture at high deposition temperatures. The grain size of ZnS increases with increasing deposition temperature. Both hardness and fracture toughness are a function of grain size and follow Hall-Petch equation. Solid particle erosion test show that the deposits obtained at high deposition temperature have more serious damage feature on the surface.The spectrum shows that the deposition temperature does not affect the transmittance in the range over 14μm as well as the long wavelength cut-off, it is caused by the extrinsic absorption in the ZnS. The IR spectrum shows that the deposit obtained at lower deposition temperature exhibit a significant 6.3μm absorption band which is caused by the Zn-H stretching in the ZnS. The Zn-H stretching could decrease the transmittance in the range of 4 to 16μm. As the deposition temperature is increased over 700℃, the 6.3μm absorption band disappears and the transmittance in the range of 4 to 16μm increases. The spectrum in short wavelength region of 0.35 to 2.5μm is affected by the grain size and pores of the ZnS. This results in that the deposits obtained at high deposition temperature has shorter cut-on wavelength and larger transmittance in the range of 0.35 to 2.5 μm.